The present invention relates to a hydrocarbon conversion process. More particularly, this invention relates to the catalytic hydrocracking of hydrocarbons.
The hydrocracking of hydrocarbons is old and well-known in the prior art. These hydrocracking processes can be used to hydrocrack various hydrocarbon fractions such as reduced crudes, gas oils, heavy gas oils, topped crudes, shale oil, coal extract and tar extract wherein these fractions may or may not contain nitrogen compounds. Modern hydrocracking processes were developed primarily to process feeds having a high content of polycyclic aromatic compounds, which are relatively unreactive in catalytic cracking. The hydrocracking process is used to produce desirable products such as turbine fuel, diesel fuel, and middle distillate products such as naphtha and gasoline.
The hydrocracking process is generally carried out in any suitable reaction vessel under elevated temperatures and pressures in the presence of hydrogen and a hydrocracking catalyst so as to yield a product containing the desired distribution of hydrocarbon products.
Hydrocracking catalysts generally comprise a hydrogenation component on an acidic cracking support. More specifically, hydrocracking catalysts comprise a hydrogenation component selected from the group consisting of Group VIA metals and Group VIII metals of the Periodic Table of Elements, their oxides or sulfides. The prior art has also taught that these hydrocracking catalysts contain an acidic support comprising a crystalline alumino silicate material such as X-type and Y-type alumino silicate materials. This crystalline aluminosilicate material is generally suspended in a refractory inorganic oxide such as silica, alumina, or silica-alumina.
The preferred Group VIA metals are tungsten and molybdenum the preferred Group VIII metals are nickel and cobalt.
The prior art has also taught that combinations of metals for the hydrogenation component, expressed as oxides and in the order of preference, are: NiO-WO.sub.3, NiO-MoO.sub.3, CoO-MoO.sub.3, and CoO-WO.sub.3.
Other hydrogenation components broadly taught by the prior art include iron, ruthenium, rhodium, palladium, osmium, indium, platinum, chromium, molybdenum, vanadium, niobium, and tantalum.
References that disclose hydrocracking catalysts utilizing nickel and tungsten as hydrogenation components, teach enhanced hydrocracking activity when the matrix or catalyst support contains silica-alumina. For instance, U.S. Pat. Nos. 4,576,711, 4,563,434, and 4,517,073 all to Ward et al., show at Table V thereof that the lowest hydrocracking activity is achieved when alumina is used in the support instead of a dispersion of silica-alumina in alumina. The lowest hydrocracking activity is indicated by the highest reactor temperature required to achieve 60 vol. % conversion of the hydrocarbon components boiling above a predetermining end point to below that end point.
Similarly, U.S. Pat. No. 3,536,605 to Kittrell et al. teaches the use of silica-alumina in the catalyst support when a nickel- and tungsten-containing hydrogenation component is employed.
U.S. Pat. No. 3,598,719 to White teaches a hydrocracking catalyst that can contain 0 wt. % silica, i.e. less than 15 wt. % silica. However this patent further requires that a crystalline molecular sieve component be present in the catalyst in an amount of 30 to 70 wt. % based on total composite weight.
As can be appreciated from the above, there is a myriad of catalysts known for hydrocracking whose catalytic properties vary widely. A catalyst suitable for maximizing naphtha yield may not be suitable for maximizing the yield of turbine fuel. Further, the degree of cracking and yield structure is also dependent upon the feedstock composition.
Catalysts of high hydrogenation activity relative to acidity yield more highly saturated products as required in distillate fuels such as jet or aviation fuel.
In accordance with the process of the present invention a feedstock containing a light catalytic cycle oil is converted into naphtha plus high quality, i.e., low aromatic content distillates. The process of the present invention provides for the production of a hydrocracked product that possesses an aromatics content low enough that the total hydrocracked product can be distilled to produce a jet fuel fraction. Heretofore known hydrocracking processes suitable for handling light catalytic cycle oils generally produced distillate products that contained high concentrations of aromatic compounds that were thus unsuitable for blending into distillate fuels. This aromatics-containing distillate had to be hydrogenated at high pressures in a subsequent separate reaction zone over a noble metal-containing catalyst to produce jet fuel or be rehydrocracked into a gasoline fraction. The present invention provides for a process that permits a "once through operation" omitting any recycle of products such that the products contain naphtha and a finished distillate fuel or a blending component thereof.